The present invention relates to axial flow machine assembly/disassembly tools and methods and, in particular, to tools for handling components, such as aerofoils, for overhaul and maintenance of axial flow machines.
In an axial flow machine, a fluid flow is directed along a course that is substantially parallel to an axis of rotation of the machine. An axial flow machine, such as a compressor, impeller, turbine or the like, may form a sub-assembly of a larger machine. The compressor of an axial flow engine is one example of such a machine and typically comprises several axially-aligned stages, with each stage designed to increase the pressure of the airflow passing therethrough. A conventional compressor may thus comprise successive arrays, often referred to as ‘rows’, of aerofoils, typically arranged as successive arrays of rotor blades with each rotor array being spaced by an intermediate array of stator vanes. The purpose of the stator arrays of aerofoils is to redirect the airflow either before or after passage through the rotator array, thereby influencing both the direction and pressure of the airflow through the compressor.
Stator arrays of aerofoils are commonly attached to the casing of the compressor, often via a common channel in the casing. Over time, and with prolonged use, aerofoils in such an array have the potential to become damaged, or otherwise need to be removed and/or replaced.
The removal of individual aerofoils from an array is a critical process in the overhaul of a gas turbine engine. As such there is a need for the process to be as streamlined and efficient as possible.
The conventional aerofoil removal process involves sliding each stator aerofoil in turn along the channel in the casing so as to remove the aerofoil from an open end of the channel. However, due to the high operating temperatures of an axial flow engine and the loading on the aerofoils in use it is possible for aerofoils to become distorted and/or slightly misaligned over time, and this can result in the aerofoils becoming stuck or jammed in their position in the casing channel. This is a particular problem due the high tolerance required between the stators and the channel. As such the force required to loosen and remove an aerofoil is increased.
A basic process for the removal of aerofoils from an axial flow engine involves attempting to loosen the aerofoil by striking it with a hammer or mallet, and then simply prying the aerofoil free by hand. The force provided by the combination of a hammer or mallet and prying the aerofoil by hand is often insufficient to remove the aerofoil. This process may need to be repeated a plurality of times, typically using varying impact forces each time, thereby making the process as a whole time-consuming and potentially causing damage to the aerofoils and/or the casing.
Furthermore, due to the variable condition that each aerofoil may be found in, each aerofoil may need to be treated differently. As such some aerofoils may have been removed with minimal force whereas other aerofoils in the same array may have undergone significant impact forces. Furthermore, the success of the entire procedure can often also depend on the experience of the fitter tasked with carrying out the procedure. Such variations in both success rate and impact forces applied are clearly undesirable for a critical process in the overhaul of a gas turbine engine.
There have been several attempts to provide alternative tools and/or systems for carrying out a stator removal procedure such that the removal process can be better controlled. Examples of such tools are disclosed in EP2169184, U.S. Pat. No. 4,096,614, and U.S. Pat. No. 8,381,379. However each of these tools has been found to have associated problems. Such tools represent large systems for accommodating the entire array and have a drive mechanism for applying force to one or more stator in a predetermined (i.e. circumferential) direction. Such complex systems are therefore difficult for a fitter to use with any real accuracy. Such tools often require that an excessive level of force is applied to remove an aerofoil from its position, and this can potentially cause damage to the aerofoil and/or casing, as well as creating potentially hazardous situations for the fitter. Furthermore, the large scale of such tools can also mean that they are expensive to manufacture.
It is an aim of the invention to provide a tool for which one or more of the problems discussed above is at least partially mitigated. It may be considered a further aim to provide a tool that can better accommodate removal of individual aerofoils from an array in a more controlled manner.